netdev - Re: [PATCH 20/21] net: warn if drivers set tx_queue

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Message-ID: <20150818181440.GB20744@orbit.nwl.cc>
Date:	Tue, 18 Aug 2015 20:14:40 +0200
From:	Phil Sutter <phil@....cc>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, brouer@...hat.com, davem@...emloft.net
Subject: Re: [PATCH 20/21] net: warn if drivers set tx_queue_len = 0

On Tue, Aug 18, 2015 at 07:47:28AM -0700, Eric Dumazet wrote:
> On Tue, 2015-08-18 at 10:30 +0200, Phil Sutter wrote:
> > Due to the introduction of IFF_NO_QUEUE, there is a better way for
> > drivers to indicate that no qdisc should be attached by default. Though,
> > the old convention can't be dropped since ignoring that setting would
> > break drivers still using it. Instead, add a warning so out-of-tree
> > driver maintainers get a chance to adjust their code before we finally
> > get rid of any special handling of tx_queue_len == 0.
> 
> How an admin can remove qdisc on a regular ethernet device with this
> schem ?
> 
> I was doing :
> 
> tc qdisc replace dev eth0 root pfifo
> ifconfig eth0 txqueuelen 0
> tc qdisc del dev eth0 root
> 
> 
> I see nothing in your patches to avoid the DEPRECATED warning.

Well, the warning is printed only upon interface registration, so
affects only drivers which set tx_queue_len = 0 by default. If you do
the above, you won't hit that check.

But you've got a point here: If we drop the special handling of
tx_queue_len == 0, there won't be any chance to change a non-virtual
interface's qdisc to noqueue anymore. This is definitely something to
reconsider before going any further.

Thanks, Phil
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